The present invention relates to a filter device structure, and more particularly, to a thin film microwave frequency acoustic filter device structure.
Filter banks are used to perform real time spectrum analysis of broad band signals. Typically, filter banks comprise individual filters that are large, expensive and are extremely difficult to manifold, especially at high frequencies. The complicated manifolding circuitry causes significant filter losses. Also, the bandwidth available with current microwave filters is too limited for effective use in filter banks. For example, the bandwidth of 2 GHz microstrip filters cannot be made less than about 8% (160 MHz) without accessive insertion losses (5 DB). Bandwidths of approximately 20 MHz can be achieved with coax filters. But, coax filters are large, cannot be manifolded easily and each pole of a coax filter requires individual adjustment.